Legal analysis: invoices can be used as the basis for collection. 1, it doesn't matter if there is no debt in the payment, but it must be signed, either on the invoice or on the receipt, or when both parties sign a contract, there must always be a place to sign. If there is no signature or debt anywhere, it is broken. Only cash transactions need not be signed, just pay off the money and goods. If there is no on-site settlement, there must be written evidence, not necessarily IOUs.

Legal basis: Article 63 of the Civil Procedure Law of People's Republic of China (PRC) includes:

(a) Statements of the parties;

(2) Documentary evidence;

(3) Physical evidence;

(4) Audio-visual materials;

(5) Electronic data;

(6) Testimony of witnesses;

(7) Appraisal opinions;

(8) Records of the inquest. Evidence must be verified before it can be used as a basis for ascertaining facts.